1. Technical Field
The present disclosure relates to an imaging device including a photoelectric converter. Further, the present disclosure relates to a signal processing circuit.
2. Description of the Related Art
Digital video cameras and digital still cameras are widely used. These cameras use CCDs (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) image sensors. The CMOS image sensors are advantageous over the CCD image sensors, for example, in terms of high-speed driving and are becoming mainstream in imaging devices (e.g., imaging elements).
In the field of imaging devices, there is a demand for higher definition. An increase in the number of pixels along with higher definition leads to a reduction in area of each pixel, and by extension, to a decrease in area of a light receiver in each pixel. The decrease in area of the light receiver leads to a reduction in sensitivity. Further, the reduction in area of each pixel leads to a reduction in amount of saturated charge in each pixel.
Japanese Unexamined Patent Application Publication No. 2011-228621 proposes a stacked imaging element. In the stacked imaging element disclosed in Japanese Unexamined Patent Application Publication No. 2011-228621, a photoelectric conversion layer including an organic photoelectric conversion film and a pixel electrode is stacked above a circuit for reading out a signal, and the circuit for reading out a signal and the pixel electrode are electrically connected to each other via a conductive plug. In the stacked imaging element, a comparatively high sensitivity and a comparatively large amount of saturated charge are easily achieved, as a larger area can be ensured for a light receiver even with a reduction in pixel size.
In the field of imaging devices, there is also a demand for a dynamic range expansion. Japanese Patents Nos. 4467542 and 4502278 propose an imaging device having a capacitive element provided in a circuit in a pixel. In the imaging element disclosed in FIG. 1 of Japanese Patent No. 4467542 and FIG. 1 of Japanese Patent No. 4502278, the amount of saturated charge is increased by connecting the capacitive element to a floating diffusion via a transistor.
However, the imaging device is also required to suppress contamination of the floating diffusion by dark-current noise, not only to expand a dynamic range.